The present invention relates, in general, to electronics, and more particularly, to methods of forming semiconductor devices and structures therefor.
In the past, the semiconductor industry utilized various design techniques to implement voltage regulators and particularly voltage regulators operating in the linear or continuous time mode. Typically, these linear voltage regulators utilized a series pass output transistor to couple an unregulated input voltage to a regulated output voltage and provide a load current that flowed from the voltage input to the voltage output. The voltage regulator usually had a control loop that included an error amplifier which was utilized for comparing the output voltage to a fixed reference voltage and driving the output transistor to maintain the regulated output voltage at a fixed voltage value. One particular application for such voltage regulators was generally referred to as low drop-out voltage regulators. Low drop-out regulators are characterized by operation with a very small difference between the unregulated input voltage and the regulated output voltage. Typically, the difference is less than about three-fourths of a volt.
One particular problem with low drop-out regulators, was oscillation. Typically, the load that was driven by the low drop-out regulator had a capacitive component. Because of phase lags in the voltage regulator control loop, oscillations tended to develop in the regulated output voltage. One method for stabilizing such control loops was to add a resistor and capacitor network in parallel with the control electrode of the output transistor. The network degraded AC parameters such as ripple rejection on the unregulated input voltage at low current levels.
Accordingly, it is desirable to have a voltage regulator having a control loop that minimizes oscillation. tendency, that provides a damping effect that assists in minimizing oscillations, and that has a wide operating range of load current without degrading regulation provided by the voltage regulator.